In perl there are two ways to represent string literals: single-quoted strings and double-quoted strings.

Single-Quoted Strings

Single quoted are a sequence of characters that begin and end with a single quote. These quotes are not a part of the string they just mark the beginning and end for the Perl interpreter. If you want a ' inside of your string you need to preclude it with a \ like this \' as you'll see below.
Let's see how this works below.

Double-Quoted Strings
Double quoted strings act more like strings in C or C++ the
backslash allows you to represent control characters. Another
nice feature Double-Quoted strings offers is variable interpolation
this substitutes the value of a variable into the string. Some examples are below

prints "blah\blah". To put a literal \ in a Perl
single-quoted string, you should use \\, just
like with double-quoted strings. If the character after
a \ (in a single-quoted string) doesn't happen to be ' or
\, then the \ is preserved. But using this fact often
leads to confusion like the mistake in your post, so I
discourage people from doing that.

I really wish Perl had used '' (two adjacents 's) to
quote ' inside of 's. But my time machine is broken.

Hi,
In the table "Some of the things you can put in a Double-Quoted String" there seems to be a typo as follows :

In your Table is :

\L lowercase all letters until \E
\U uppercase all letters until \E
\Q Backslash quote all nonletters and nonnumbers until \E
\E Stop \U \L or \E
It seems that the line \E Stop \U \L or \E should read
\E Stop \U \L or \Q .
Otherwise it means the \E stops it self .